A region/patch of space-time is also a space-time.

[Audio] In physics, spacetime is a mathematical model that combines the three dimensions of space and one dimension of time into a single four-dimensional manifold. Each point in this manifold corresponds to an event in reality. Basically point p1 (x,y, z,t) will be an event happening in space co-ordinates x,y,z and time t according to a frame of reference. A region or patch in spacetime is also a spacetime because it has 3 space dimensions and 1 time dimension and a point on that region of space time corresponds to an event in the reality happening on the space and time co-ordinates defined in that region. Think of it like this:- A subset of a line-segment is also a line-segment or a subset of an arc is also an arc, a region of a surface is also a surface. In fact, Einstein's general relativity uses the same concept. It divides a curved spacetime into infinitesimal regions of flat spacetimes and uses special relativity on those flat spacetimes..